5 Answers

I seem to remember hearing that it had something to do with the calendar changing – the 31st was added into March, so people who’d forgotten about the change walked around thinking that it was April 1st when it was really the newly-created March 31st. Those people were known as “April Fools”.

Whether that story has any truth? I doubt it. It’s just what I remember being told or having read long long ago.